How can I make a timer?
Depends what you mean when you say timer. If you want a timer during your animation your best bet is to just calculate the corresponding keyframe. If you mean just a generic timer, the easiest way from within python is with threading. 

import threading

def foo():
    print("times up")

timer = threading.Timer(7*60, foo)
timer.start()


see https://docs.python.org/3/library/threading.html#timer-objects for more details